Electromagnetic fuel injection valves are gaining wide acceptance in the fuel metering art for both multi-point and single point systems where an electronic control system produces a pulse width signal representative of the quantity of fuel to be metered to an internal combustion engine. These injectors operate to open fuel metering orifices leading to the air ingestion paths of the engine by means of a solenoid actuated armature responding to the electronic signal. Because of recent advances, these injectors are becomming very precise in their metering qualities and very fast in their operation. With these advantages, the electromagnetic fuel injector valve will continue to assist the advances in electronic fuel metering which improve economy, reduce emissions, and aid drivability of the internal combustion engine.
The electromagnetic injector valve is, however, relatively expensive to manufacture because of a precision metering portion which must be carefully coupled to a magnetic motor circuit and, thereafter, to an electrical control while being contained in a single injector body. All of these sections must cooperate properly for the valve to provide maximum performance and should be contained in the minimum space. It is important in single point metering applications where the injector is mounted above the throttle plate that the injector package not block air flow into the air ingestion bore.
The injector body manufacture has been one contributor to the expense of manufacturing an injector valve. Generally, the injector body is manufactured from a cylindrical metal blank by a plurality of automatic machining operations. The most common configuration is a plurality of differently stepped or diametered bores which are machined to close tolerances and which form shoulders at the steps with the bores coaxial to each other. Such an injector body is illustrated in a U.S. Pat. No. 3,967,597 issued to Schlagmuller. The close tolerance or the depth of the bores in relationship to the others are used to locate other points of the injector, such as the valve closure portion precisely with respect to the moving section of the valve which contains the armature and stator.
Usually, all the bores are coaxial because the fluid flow path is centrally located through the valve and the needle valve is biased against a conical seat and should have an equal peripheral sealing pressure around the seat. The precision of the depth of the multiple step bores, their coaxial relationship, and their number generally requires that the injector body has to be chucked or remounted more than once during the machining operation which adds expense to the manufacturing costs. An injector that could be manufactured from parts requiring only a single machining operation or by eliminating altogether a part requiring multiple machining operations would be desirable.
The static and dynamic fuel flow characteristics are important to the operation of the injector valve and are controlled by a number of different parameters. In an electromagnetic valve, to provide a fast acting valve with a stable dynamic fuel flow, the opening and closing times must be minimized but kept relatively certain and reproducible. One factor directly influencing the opening and closing times of the injector is the closure force that the valve spring applies to the needle valve. The amount of spring pressure is linearly related to the amount the spring is compressed, or F=Kx where x is the compression distance. The higher the closure force, the slower the opening time of the valve will be, and, conversely, the faster the valve will close.
Another interrelated factor is the distance through which the magnetic force acts upon the armature, and thus, the amount of travel the needle valve takes from the valve seat, or, as it is commonly called, the lift of the valve. The longer the lift or the greater the air gap, the slower the valve will open. At the other extreme, there is a minimum air gap that should be maintained to allow the collapse of the magnetic field when the injector is deenergized. If the minimum gap is not maintained during operation, the armature will tend to stick to the stator, and thus, affect the closing time of the valve.
In many prior art valves the lift is designed to be greater than that which would restrict static fuel flow. Therefore, the size of the metering orifice is designed to be the only controlling factor of flow rate when the valve is open. This is not an optimal design because the lift is greater than necessary thereby affecting the opening time of the valve, and a valuable control parameter for regulating the static flow rate has not been utilized.
In the Schlagmuller reference, the lift of the prior art valve is controlled by a spacer collar abutting a precisely machined spacer washer of a fixed thickness and the spring pressure force is adjusted upon assembly of the valve by axial movement of the core member which is then pinned to fix the pressure. In this valve the lift is structurally set and subsequently the spring pressure adjusted and fixed during assembly to a set value. The lift is such that static fuel flow is controlled only by the size of the metering orifice. These valves which have a static fuel flow out of tolerance must be disassembled and their metering orifices rebored.
It would be highly desirably, since the two factors of lift and closure forces are very much related to static fuel metering and the speed of valve operation, if they could be independently adjusted so as to complement each other. Further, it would be advantageous to adjust these characteristics of the electromagnetic injector valve after assembly to precisely tailor each valve characteristic.
Another problem that has affected the speed of operation and reproducible opening and closing times of the electromagnetic injector valve has been the eccentric loads from the closure spring whereby the needle valve has a component or plurality of force components applied to it not acting coaxially to the spray axis. This causes wear on the bearing surfaces which hold the needle coaxial with the spray axis and frictional spots where the valve hesitates as it moves within the valve housing. The long moment arm through which the closure spring acts is primarily responsible for the eccentric loads. The closure force is usually applied to the armature at the point on the needle valve farthest from the valve seat which acts as a fulcrum. Any axial offset force is magnified by the moment arm and must be absorbed and balanced by the needle valve bearing surfaces.
Torsional or windup pressures on the closure spring will also produce a change in the force provided against the needle valve. If possible, while adjusting the spring pressure, winding the spring or providing a torsional component to the closure force should be avoided and only substantially coaxial compression should be applied to the closure spring.
Another problem that has occured in single point electromagnetic injector valves with fuel inlets located substantially at the valve end is that fuel will be drawn up the guide bore of the armature and into the air gap between the core member and the armature when movement between them occurs. As the guide bore and armature form a relatively small clearance so as to maintain the needle coaxial, fuel that finds its way into the air gap will build up pressure due to the pumping action of the armature against the core. This phenomenon of increasing hydraulic pressure at the interface of the movement will cause a slowing in the opening time of the valve. In this type of single point injector it would be highly desirably to provide a means to relieve this pressure so as not to create any detrimental affects on the dynamic operation of the valve.
As the electromagnetic fuel injector is accepted in wide-spread use, there will have to be an extension of the environmental temperature range over which it is operational. One present limitation of prior art valves has been their cold temperature operation because of the sealing properties of the O-rings contained therein. Generally, the O-rings are elastomeric rings of rubber or material which remains substantially flexible at normal ambient temperatures or increased temperatures. They seal relatively well between the dissimilar materials of the injector body and the bobbin which expand and contract at different volumetric rates. However, at colder temperatures, especially in the ranges beyond -20.degree. F., they start to become inflexible and fairly brittle. At this point the dissimilar contraction rates between the bobbin and injector body will cause a separation between the O-ring and its interface and consequent leakage of pressurized fuel. It would be advantageous to provide an injector with an extended cold temperature range whereby the O-ring sealing structure could be extended in operation to approximately -40.degree. F.